In the modern medicine, knowledge has been disseminated on a technology in which: a fluorescent substance is administered to a patient; when the fluorescent substance is accumulated in an affected area to a certain amount, the affected area is irradiated with an excitation light whose wavelength can excite the fluorescent substance; thereby, fluorescent light is emitted only from the affected area; and thus, fluorescence observation and fluorescence photography are applied to the affected area by use of an optical filter which transmits only the fluorescent light.
5-aminolevulinic acid (5-ALA), talaporfin sodium (whose registered trademark is Laserphyrin), indocyanine green (ICG) and the like are known as fluorescent substances. 5-aminolevulinic acid emits fluorescent light with a wavelength of approximately 620 nm when receiving excitation light with a wavelength of approximately 380 nm. Talaporfin sodium emits fluorescent light with a wavelength of approximately 672 nm when receiving excitation light with a wavelength of approximately 664 nm. Indocyanine green emits fluorescent light with a wavelength of approximately 835 nm when receiving excitation light with a wavelength of approximately 805 nm. Indocyanine green is the closest to infrared light.
The above excitation light is also used as illumination light for a microscope which observes the affected area. In other words, illumination light for observing the affected area with the microscope is irradiated on the affected area from the beginning, and the illumination light is used as the excitation light. The microscope is supported by an arm of a stand device, and an irradiation hole is formed in the bottom surface of the microscope. The illumination light is supplied to the microscope from a light generating unit through an optical fiber, and is thus irradiated onto the affected area from the irradiation hole of the microscope. The light generating unit is installed inside or outside the main body of the stand device. A xenon lamp or a halogen lamp being capable of emitting white light close to solar light and having good color rendering properties is generally used as a source of light used in the light generating unit.
The light generating unit is provided with: a thermally-protective optical filter configured to cut wavelengths in the infrared region, which become heat radiation on the affected area, from the illumination light; and a fluorescence filter configured to selectively transmit only excitation light, whose wavelength corresponds to the fluorescent substance, from the illumination light from the source of light. One of these two optical filters selectively intervenes in the optical path of the illumination light from the source of light while sliding or revolving into the optical path. Usually, the thermally-protective optical filter intervenes in the optical path, and thereby transmits visible light and cuts infrared light. During a fluorescence observation, the fluorescence optical filter intervenes in the optical path, and thus selectively transmits only excitation light whose wavelength corresponds to the fluorescent substance (see Patent Document 1).
[Patent Document 1] Japanese Patent Application No. 2004-163413.